150 THE CHEMISTRY OF CATTLE FEEDING 



in soft clay soil, it is more considerable. In any case it can 

 be measured and expressed in pounds weight ; but it must be 

 noted that the draught is the pressure on the collar, not the 

 mass of substance moved, except when the work is done 

 wholly against gravity. 



When an unharnessed horse walks or runs along the level 

 there is no draught and no load, yet it does work ; and if it 

 continue all day, the work will amount to many foot-pounds. 

 In this case the effort, P, is represented by the work of moving 

 the animal's body through space. This may be put at about 

 one-twentieth of the weight of the animal. Thus in the case of 

 an unharnessed horse TOGO Ibs. live weight, trotting at 7 miles 

 per hour for i hour, the work would amount to 1*848 million 

 foot-pounds, and at 10 miles per hour it would be 2*64 million 

 foot-pounds. 



When the animal carries a load on its back, this must be 

 added to the weight of the animal. For example, suppose 

 the weight of the saddle and rider were together equal to 

 200 Ibs., the total effort would be equivalent to a draught of 

 60 Ibs., whereas when the animal goes without .any load, the 

 effort is only equivalent to a draught of 50 Ibs. In short, 



in the case of an animal without any load the effort, P, is , 



20 



and with a load it is L, where M is the live weight (in 



pounds) of the animal, and I, is the weight (in pounds) of the load. 

 The three graphs drawn in the diagram (Fig. IT) show, 

 respectively, the amount of work done in i hour by a horse of 

 1000 Ibs. live weight, (a) when going at different speeds with- 

 out any load or draught, (b) when carrying different loads on 

 its back at a constant speed of 5 feet per second (3-4 miles 

 per hour), (c) when going against different draughts at the 

 same constant speed (3-4 miles per hour). The three graphs 

 show the effect, on the total work done, of the given incre- 

 ments of speed, load, and draught respectively ; but, of course, 

 if the horse were of a different size or if different increments 

 were assumed, the graphs would not bear the same relation to 

 each other. 



